Method and apparatus for monitoring and controlling imaging in immersion lithography systems

Abstract

A method of monitoring an immersion lithography system in which a wafer can be immersed in a liquid immersion medium for exposure by an exposure pattern. The method detects the presence of a foreign body in the immersion medium to thereby determine if the immersion medium in a state that is acceptable for exposing the wafer with the exposure pattern. Also disclosed is a monitoring and control system for an immersion lithography system.

1. A method of monitoring an immersion lithography system, comprising:
 immersing at least a portion of a wafer to be exposed in a liquid immersion medium; 
 directing a laser beam through a volume of the immersion medium through which an exposure pattern is configured to traverse; and 
 determining if a portion of the laser beam beyond a predetermined threshold value becomes scattered, thereby indicating that a foreign body is present in the traversal volume and the immersion medium is in a state that is unacceptable for exposing the wafer with the exposure pattern. 
 
     
     
       2. The method according to  claim 1 , further comprising exposing the wafer with the exposure pattern if the determining indicates that a scattered portion of the laser beam is less than the predetermined threshold value. 
     
     
       3. The method according to  claim 1 , wherein the determining is carded out by detecting scattered light segment separated from the laser beam by an encounter of the laser beam with a foreign body and analyzing information relating to the detected scattered light segment. 
     
     
       4. The method according to  claim 3 , wherein the information relating to the detected scattered light segment is at least one of an intensity of the scattered light segment or a location of the scattered light segment. 
     
     
       5. The method according to  claim 1 , wherein the determining is carried out by detecting the laser beam after the laser beam exits the traversal volume and analyzing information relating to the detected laser beam to determine if the laser beam encountered a foreign body and became diminished. 
     
     
       6. The method according to  claim 5 , wherein the information relating to the laser beam is indicative of an encountered foreign body if at least one of an intensity of the laser beam incident on a detecting assembly is less than expected or a location of the laser beam incident on detecting assembly is different than expected. 
     
     
       7. The method according to  claim 1 , wherein the entire traversal volume is monitored for the presence of the foreign body. 
     
     
       8. The method according to  claim 7 , wherein multiple laser beams are used to monitor for the presence of the foreign body. 
     
     
       9. The method according to  claim 7 , wherein at least one laser beam is scanned through the traversal volume to monitor for the presence of the foreign body. 
     
     
       10. The method according to  claim 1 , further comprising controlling the immersion lithography system to defer exposing the wafer if the immersion medium is in the state that is unacceptable for exposing the wafer with the exposure pattern. 
     
     
       11. The method according to  claim 10 , wherein the immersion lithography system is controlled to wait a predetermined period of time and repeat the directing and determining if the immersion medium is in the state that is unacceptable for exposing the wafer with the exposure pattern. 
     
     
       12. The method according to  claim 10 , wherein an immersion medium control subsystem is commanded to take corrective action if the immersion medium is in the state that is unacceptable for exposing the wafer with the exposure pattern. 
     
     
       13. The method according to  claim 1 , wherein the foreign body is at least one of a particle or a bubble. 
     
     
       14. A monitoring and control system for an immersion lithography system, the immersion lithography system including a chamber for receiving a wafer to be exposed and immersing at least a portion of the wafer in an immersion medium and an imaging subsystem for directing an exposure pattern towards the wafer and through the immersion medium, comprising:
 an immersion medium monitoring subsystem including a laser for directing a laser beam through a volume of the immersion medium through which the exposure pattern is configured to traverse, and a detector assembly for receiving the laser beam after the laser beam exits the traversal volume and for outputting a signal containing information indicative of the presence or absence of a foreign body in the immersion medium; and 
 a controller, the controller receiving and analyzing the signal to determine if the immersion medium is in a state that is acceptable for exposing the wafer with the exposure pattern. 
 
     
     
       15. The monitoring and control system according to  claim 14 , wherein the controller controls the immersion lithography system to expose the wafer with the exposure pattern if the determining indicates that a scattered portion of the laser beam is less than the predetermined threshold value. 
     
     
       16. The monitoring and control system according to  claim 14 , wherein the determining is carried out by detecting a scattered light segment separated from the laser beam by an encounter of the laser beam with a foreign body and analyzing information relating to the scattered light segment. 
     
     
       17. The monitoring and control system according to  claim 16 , wherein the information relating to the detected scattered light segment is at least one of an from intensity of the scattered light segment or a location of the scattered light segment. 
     
     
       18. The monitoring and control system according to  claim 14 , wherein the determining is carried out by detecting the laser beam after the laser beam exits the traversal volume and analyzing information relating to the detected laser beam to determine if the laser beam encountered a foreign body and became diminished. 
     
     
       19. The monitoring and control system according to  claim 18 , wherein information relating to the laser beam is indicative of an encountered foreign body if at least one of an intensity of the laser beam incident on the detector assembly is less than expected or a location of the laser beam incident on the detector assembly is different than expected. 
     
     
       20. The monitoring and control system according to  claim 14 , wherein the controller controls the immersion lithography system to defer exposing the wafer if the immersion medium is in the state that is unacceptable for exposing the water with the exposure pattern. 
     
     
       21. The method according to  claim 1 , wherein the determining is conducted to monitor specifically for one or more bubbles present in the traversal volume. 
     
     
       22. The monitoring and control system according to  claim 14 , wherein the immersion medium monitoring subsystem and the controller are coordinated with each other to monitor specifically for one or more bubbles present in the traversal volume.